1. Field of the Invention
The invention relates to a fuel injection apparatus for internal combustion engines in which a control valve unit for metered fuel injection is inserted into a fuel conduit from a high-pressure fuel source to an injection opening.
2. Description of the Prior Art
Fuel injection apparatuses of this type with which this invention is concerned, known from the prior art, are particularly used in common rail systems to control the supply of fuel to the injection opening, which is usually embodied as a nozzle holder device, generally by means of a slide valve or seat/slide valve, which can be embodied as force-compensated or partially force-compensated.
These known slide valves or seat/slide valves have control edges for covering and uncovering inlets and outlets, where the usually small overlaps result in large leakage fuel flows inside the slide valves, which has a disadvantageous effect on the injection of fuel into a combustion chamber of an internal combustion engine.
For this reason, there has been a transition to the use of double seat valves for the controlled injection of fuel, which have the advantage over slide valves that a stroke length is considerably increased and a high degree of sealing action at the valve seats can be achieved. Double seat valves also have the advantage over slide valves that the stroke length in a double seat valve can, on the other hand, be selected to be small so that the double seat valve can be directly controlled by a piezoelectric unit while complying with the requirement for a force-compensated or partially force-compensated valve.
DE 198 60 678 has disclosed a fuel injection apparatus for internal combustion engines in which a fuel injection valve is supplied with fuel by means of a high-pressure line. This known fuel injection apparatus has an injection valve member, which is for controlling an injection opening and whose axial movement in an injection valve bodyxe2x80x94and therefore the opening of the injection nozzlexe2x80x94is controlled by a control unit, which is embodied as a piezoelectric actuator and can be used to actuate the injection valve member.
The injection valve member is embodied with a valve head, which cooperates with two valve seats of the injection valve body of the control valve unit in such a way that when electrical voltage is applied to the piezoelectric actuator, this permits a flow of fuel, which is conveyed from the high-pressure fuel source by means of a high-pressure line, via the first valve seat and the second valve seat, through the fuel injection valve, and into an additional high-pressure line leading to the injection opening.
However, it has proven to be disadvantageous that it is particularly difficult to produce the complex design of the valve housing and the injection valve body, with numerous mold joints in the assembly of a force-compensated or partially force-compensated valve with a multi-part valve body.
The fuel injection apparatus for internal combustion engines according to the invention has the advantage that the control valve unit has outwardly opening first valve seat on the outer diameter of the valve body and an inwardly opening second valve seat, which valve seats do not have to face each other with regard to the orientation, as a result of which the control valve unit has a design that is very easy to manufacture from a production engineering standpoint. This arrangement affords significant latitude in manufacturing tolerances, which reduces production costs.
It is also advantageous that the control valve unit is provided in the form of a precisely functioning 3/2-way valve in a pressure-controlled system, which valve can be directly actuated preferably by a piezoelectric actuator unit, were the integration of the control valve unit into the inlet of fuel into the injection opening of the fuel injection apparatus permits short injections that can be precisely metered.
One significant advantage of the fuel injection apparatus according to the invention is represented by the design of the control valve unit with a closing device on the side of the valve member oriented away from the piezoelectric unit, since this closing device, due to its design with a closing body and a closing element disposed between the closing body and the valve member, is self-centering, as a result of which only minimal demands have to be placed on the manufacturing tolerances.